Optical, magnetic and magneto-optic data storage media are examples of high performance data storage technologies. Each of these data storage technologies exhibits a relatively high storage capacity coupled with a relatively low cost per megabyte of data stored. The use of optical data storage media has become widespread in audio, video and computer data applications, including the use of the compact disc (CD), the digital versatile disc (DVD), multi-layer structures (such as DVD-5 and DVD-9), multi-sided structures (such as DVD-10 and DVD-18), the magneto-optic disc (MO), other write-once and re-writable formats (such as CD-R, CD-RW, DVD-R, DVD-RW, DVD+RW and DVD-RAM) and the like, collectively referred to herein as “data storage media”. In each of these formats, data is encoded onto a substrate in a digital data series. For example, in pre-recorded optical data storage media, such as the CD, the data is encoded into a plurality of pits and grooves formed on the surface of a plastic substrate via injection molding, stamping or the like.
In various applications, it is desirable to have a data storage medium with a limited life. For example, music, movies and video games are often rented to customers for a predetermined period of time. At the end of this predetermined period of time, the customer must return the rented item to the renter. As a result, the renter must keep track of each rented item. This tracking function is labor intensive, time consuming and expensive. Further, rented items are susceptible to damage by customers. Likewise, sample computer programs are often provided to potential customers in order to entice them to purchase the computer programs. These “demo” programs must, by their nature, have a limited life. Thus, it is desirable to have limited play data storage media.
There are several conventional methods for manufacturing limited play data storage media. One method includes forming a disc wherein the reflective layer is protected with a porous layer such that the reflective layer becomes oxidized over a predetermined period of time. Once the reflective layer attains a given level of oxidation, the disc is no longer readable. Another method includes depositing a coating containing a reactive dye and, optionally, one or more other additives on the surface of the disc. Upon exposure to oxygen, the reactive dye, which is initially colorless, is oxidized to form an opaque or semi-opaque layer over a predetermined period of time, rendering the disc unreadable. Alternatively, a layer containing the reactive dye is “sandwiched” between the other layers of the disc.
The problem with each of the conventional methods for manufacturing limited play data storage media is that the method is “defeatable”. In other words, individuals and cottage industries may alter the associated data storage medium such that it has unlimited playability. For example, the reactive dye method may be defeated by photo-bleaching the opaque or semi-opaque layer. Although various additives have been used to reduce the threat of photo-bleaching, none provide adequate security. Thus, a true limited play data storage medium has not yet been attained and music companies, movie studios, video game manufacturers, software manufacturers and the like do not have adequate protection for their intellectual property.